Power transistor with distributed diodes

ABSTRACT

An electronic circuit is disclosed. The electronic circuit includes a distributed power switch. In some embodiments, the electronic circuit also includes one or more of a distributed gate driver, a distributed gate pulldown device, a distributed diode, and a low resistance gate and/or source connection structure. An electronic component comprising the circuit, and methods of manufacturing the circuit are also disclosed.

REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patentapplication Ser. No. 62/039,742, entitled “POWER TRANSISTOR WITHDISTRIBUTED SCHOTTKY DIODE AND LOW Rg” filed on Aug. 20, 2014, which ishereby incorporated by reference in its entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to transistors and in particularto power transistors formed in GaN-based technologies.

BACKGROUND OF THE INVENTION

Electronic devices such as computers, servers and televisions, amongothers, employ one or more electrical power conversion circuits toconvert one form of electrical energy to another. The efficiency of thisconversion is critical to avoid wasted energy and reduce waste heatgeneration. An example of a circuit topology that requires highfrequency switching is a half bridge converter. New components withhigher speed and efficiency are needed for converter circuits to meetthe needs of new electronic devices. In addition, power transistors thatcan switch extremely fast are needed to enable frequency to increasewithout loss of efficiency. High frequency switching will reduce thesize and cost of power electronic systems. However, conventional devicesrely on drivers that are external to chip, and usually also to thepackage that houses the power transistor. In addition, the routing ofinterconnect on chip is inefficient, resulting in a gate resistance thatis usually in the range of 1-10 ohms, which limits the switching speedand efficiency. GaN technology enables power transistors to be designedthat are much smaller than conventional silicon devices, and capacitancecan be reduced by 10-20 times. Because of this, GaN devices switchextremely fast, which can be hard to control with conventional gatedrive circuits. It is essential to reduce the impedance between thedriver and the power transistor as low as possible to enable goodcontrol of the switching operation.

SUMMARY OF THE INVENTION

One inventive aspect is an electronic circuit. The electronic circuitincludes a substrate including GaN, and a distributed power switchformed on the substrate, where the distributed power switch includes aplurality of power sub-transistors, and where each power sub-transistorincludes a gate, a source, and a drain. The electronic circuit alsoincludes a distributed diode formed on the substrate. The distributeddiode includes a plurality of sub-diodes, where each sub-diode includesan anode, and a cathode. The anodes of the sub-diodes are each connectedto a source of one or more corresponding power sub-transistors, and thecathodes of the sub-diodes are each connected to a drain of one or morecorresponding power sub-transistors.

Another inventive aspect is an electronic component, including a packagebase, and at least one GaN-based die secured to the package base andincluding an electronic circuit. The electronic circuit includes asubstrate including GaN, and a distributed power switch formed on thesubstrate, where the distributed power switch includes a plurality ofpower sub-transistors, and where each power sub-transistor includes agate, a source, and a drain. The electronic circuit also includes adistributed diode formed on the substrate. The distributed diodeincludes a plurality of sub-diodes, where each sub-diode includes ananode, and a cathode. The anodes of the sub-diodes are each connected toa source of one or more corresponding power sub-transistors, and thecathodes of the sub-diodes are each connected to a drain of one or morecorresponding power sub-transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic of a half bridge power conversioncircuit.

FIG. 2 is a schematic illustration of a distributed transistor.

FIGS. 3A and 3B are schematic illustrations of a portion of anembodiment of a layout of a distributed transistor.

FIGS. 4A-4D are schematic illustrations of a portion of an embodiment ofa layout of a distributed transistor.

FIG. 5 is a schematic illustration of a distributed transistor having adistributed driver or driver output stage.

FIG. 6 is a schematic illustration of portion of an embodiment of alayout of a distributed transistor and distributed driver or driveroutput stage.

FIG. 7 is a simplified schematic of a half bridge power conversioncircuit having been modified to include a low side pulldown FET and ahigh side pulldown FET.

FIG. 8 is a schematic illustration of a circuit having a distributedtransistor and a distributed pulldown FET.

FIG. 9 a schematic illustration of an embodiment of a layout of thecircuit of FIG. 8.

FIG. 10 is a schematic illustration of a circuit having a distributedtransistor and pulldown FET, a distributed pulldown FET driver, and adistributed transistor driver.

FIG. 11 is a schematic illustration of a circuit, which includes a drivetransistor, a pulldown FET, and an inverter.

FIG. 12 is a simplified schematic of a half bridge power conversioncircuit having been modified to include clamping diodes.

FIG. 13 is a schematic illustration of a circuit having a distributedtransistor and a distributed diode.

FIG. 14 is a schematic illustration of a portion of an embodiment of alayout of the circuit of FIG. 13.

FIG. 15 a schematic illustration of a cross section of the portionillustrated in FIG. 14.

FIG. 16 a schematic illustration of a cross section of the portionillustrated in FIG. 14.

FIG. 17 is a flowchart diagram illustrating an embodiment of a method offorming a distributed transistor integrated with a distributed driver.

FIG. 18 is a flowchart diagram illustrating an embodiment of a method offorming first and second distributed transistors.

FIG. 19 is a flowchart diagram illustrating an embodiment of a method offorming first and second distributed transistors.

FIG. 20 is a flowchart diagram illustrating an embodiment of a method offorming a distributed transistor.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the present invention are implemented in halfbridge power conversion circuits that employ one or more gallium nitride(GaN) devices. While the present invention can be useful for a widevariety of circuits, some embodiments of the invention are particularlyuseful for half bridge circuits designed to operate at high frequenciesand/or high efficiencies with integrated driver circuits, integratedlevel shift circuits, integrated bootstrap capacitor charging circuits,integrated startup circuits and/or hybrid solutions using GaN andsilicon devices.

Now referring to FIG. 1, in some embodiments, circuit 100 may include apair of complementary power transistors (also referred to herein asswitches) that are controlled by one or more control circuits configuredto regulate power delivered to a load. In some embodiments a high sidepower transistor is disposed on a high side device along with a portionof the control circuit and a low side power transistor is disposed on alow side device along with a portion of the control circuit, asdescribed in more detail below.

The integrated half bridge power conversion circuit 100 illustrated inFIG. 1 includes a low side GaN device 103, a high side GaN device 105 aload 107, a bootstrap capacitor 110 and other circuit elements, asillustrated and discussed in more detail below. Some embodiments mayalso have an external controller (not shown in FIG. 1) providing one ormore inputs to circuit 100 to regulate the operation of the circuit.Circuit 100 is for illustrative purposes only and other variants andconfigurations are within the scope of this disclosure.

In one embodiment, low side GaN device 103 may have a GaN-based low sidecircuit 104 that includes a low side power transistor 115 having a lowside control gate 117. Low side circuit 104 may further include anintegrated low side transistor driver 120 having an output 123 connectedto low side transistor control gate 117. In another embodiment high,side GaN device 105 may have a GaN-based high side circuit 106 thatincludes a high side power transistor 125 having a high side controlgate 127. High side circuit 106 may further include an integrated highside transistor driver 130 having an output 133 connected to high sidetransistor control gate 127.

A voltage source 135 (also known as a rail voltage) may be connected toa drain 137 of high side transistor 125, and the high side transistormay be used to control power input into power conversion circuit 100.High side transistor 125 may further have a source 140 that is coupledto a drain 143 of low side transistor 115, forming a switch node 145.Low side transistor 115 may have a source 147 connected to ground. Inone embodiment, low side transistor 115 and high side transistor 125 maybe GaN-based enhancement-mode field effect transistors. In otherembodiments low side transistor 115 and high side transistor 125 may beany other type of device including, but not limited to, GaN-baseddepletion-mode transistors, GaN-based depletion-mode transistorsconnected in series with silicon based enhancement-mode field-effecttransistors having the gate of the depletion-mode transistor connectedto the source of the silicon-based enhancement-mode transistor, siliconcarbide based transistors or silicon-based transistors.

In some embodiments high side device 105 and low side device 103 may bemade from a GaN-based material. In one embodiment the GaN-based materialmay include a layer of GaN on a layer of silicon. In further embodimentsthe GaN based material may include, but not limited to, a layer of GaNon a layer of silicon carbide, sapphire or aluminum nitride. In oneembodiment the GaN based layer may include, but not limited to, acomposite stack of other III nitrides such as aluminum nitride andindium nitride and III nitride alloys such as AlGaN and InGaN. Infurther embodiments, GaN-based low side circuit 104 and GaN-based highside circuit 106 may be disposed on a monolithic GaN-based device. Inother embodiments GaN-based low side circuit 104 may be disposed on afirst GaN-based device and GaN-based high side circuit 106 may bedisposed on a second GaN-based device. In yet further embodiments,GaN-based low side circuit 104 and GaN-based high side circuit 106 maybe disposed on more than two GaN-based devices. In one embodiment,GaN-based low side circuit 104 and GaN-based high side circuit 106 maycontain any number of active or passive circuit elements arranged in anyconfiguration.

In some embodiments, half bridge power conversion circuit 100 is formedare on a GaN-based die secured to a package base of an electronic powerconversion component. In some embodiments, the component includesmultiple GaN-based die secured to the package base.

The components of integrated half bridge power conversion circuit 100may include features as described in further detail in U.S. applicationSer. No. 14/737,259, filed Jun. 11, 2015, which is incorporated hereinin its entirety for all purposes.

In some embodiments of integrated half bridge power conversion circuit100, either or both of power transistors 115 and 125 may be implementedwith a distributed or fingered topology. For example, FIG. 2 is aschematic illustration of a transistor 200 having such a topology.Transistor 200 includes three sub-transistors 202, 204, 206, and 208. Asshown, sub-transistors 202, 204, 206, and 208 have their respectivedrains, gates, and sources connected respectively to nodes D, G, and S,which respectively correspond with the drain, gate, and source oftransistor 200.

FIGS. 3A and 3B are schematic illustrations of a portion 220 of anembodiment of a layout of transistor 200. The embodiment of FIGS. 3A and3B is provided as an example only. Numerous alternative layoutconfigurations for transistor 200 are additionally contemplated.

Source electrode fingers 242, 244, 246, and 248 each form an ohmiccontact with the underlying AlGaN or similar layer 224 on substrate 222and collectively form the source electrode of transistor 200. Sourceelectrode fingers 242, 244, 246, and 248 respectively form the sourceelectrodes of sub-transistors 202, 204, 206, and 208. The sourceelectrode fingers 242, 244, 246, and 248 are electrically connected toone another and to one or more pins through one or more conductors (notshown). In some embodiments, such as those discussed in more detailbelow, source electrode fingers 242, 244, 246, and 248 are electricallyconnected to one another and to one or more pins through overlyingmetallization layers.

Drain electrode fingers 252, 254, 256, and 258 each form an ohmiccontact with the underlying AlGaN or similar layer 224 on substrate 222and collectively form the drain electrode of transistor 200. Drainelectrode fingers 252, 254, 256, and 258 respectively form the drainelectrodes of sub-transistors 202, 204, 206, and 208. The drainelectrode fingers 252, 254, 256, and 258 are electrically connected toone another and to one or more pins through one or more conductors (notshown). In some embodiments, such as those discussed in more detailbelow, drain electrode fingers 252, 254, 256, and 258 are electricallyconnected to one another and to one or more pins through overlyingmetallization layers.

Gate electrode fingers 232, 234, 236, and 238 are separated from AlGaNor similar layer 224 by respective gate structures. Gate structurescorresponding with insulated gates, Schottky gates, PN gates, recessedgates, and other gates may be used. Gate electrode fingers 232, 234,236, and 238 collectively form the gate electrode of transistor 200, andrespectively form the gates electrodes of sub-transistors 202, 204, 206,and 208. Gate electrode fingers 232, 234, 236, and 238 are electricallyconnected to one another and to one or more pins through one or moreconductors (not shown). In some embodiments, such as those discussed inmore detail below, gate electrode fingers 232, 234, 236, and 238 areelectrically connected to one another and to one or more pins throughoverlying metallization layers.

Field plate electrode fingers 262, 264, 266, and 268 are separated fromAlGaN or similar layer 224 by respective insulation structures, andcollectively form a field plate electrode of transistor 200. Field plateelectrode fingers 262, 264, 266, and 268 respectively form field plateelectrodes of sub-transistors 202, 204, 206, and 208. Field plateelectrode fingers 262, 264, 266, and 268 are electrically connected toone another and to one or more pins through one or more conductors (notshown). In some embodiments, such as those discussed in more detailbelow, field plate electrode fingers 262, 264, 266, and 268 areelectrically connected to one another and to one or more pins throughoverlying metallization layers.

FIGS. 4A-4D are schematic illustrations of an embodiment of a particularone of the sub-transistors of FIGS. 3A and 3B having additionalmetallization. The additional metallization forms electrical connectionsbetween pins and the source electrode finger 248, drain electrode finger258, gate electrode finger 238, and field plate electrode finger 268 ofthe underlying sub-transistor. The additional metallization layers maybe particularly advantageous for circuits such as half bridge powerconversion circuit 100. In some embodiments, the effective gate and/orsource resistance of low side transistor 115 and high side transistor125 may be reduced by use of additional metal layers connecting the gateand/or source fingers of low side transistor 115 and high sidetransistor 125. The reduced gate and/or source resistance results in,for example, faster switching times.

FIG. 4A is a cross sectional view of the one particular sub-transistor.

A first metal layer, overlying and separated from the sub-transistor byone or more insulators, is formed so as to have metal 1 structures 255,245 a, and 245 b. Metal 1 structure 255 is electrically connected withdrain electrode finger 258 through one or more vias (not shown). Metal 1structure 245 a is electrically connected with field plate electrodefinger 268 through one or more vias (not shown). Metal 1 structure 245 bis electrically connected with source electrode finger 248 through oneor more vias (not shown). The first metal layer may, for example, be0.5-2 microns thick and may comprise aluminum or copper. The first metallayer may comprise other metallic or non-metallic conductive materials.

A second metal layer, overlying and separated from the first metal layerand the sub-transistor by one or more insulators, is formed so as tohave metal 2 structures 257, 247, and 237. Metal 2 structure 257 iselectrically connected with metal 1 structure 255 through one or morevias (not shown). Metal 2 structure 247 is electrically connected withmetal 1 structures 245 a and 245 b through one or more vias (not shown).Metal 2 structure 237 is electrically connected with gate electrodefinger 238 as discussed below with reference to FIGS. 4B-4D. The secondmetal layer may, for example, be greater than 2 microns thick and maycomprise aluminum or copper. The second metal layer may comprise othermetallic or non-metallic conductive materials.

FIG. 4B is a plan view of source electrode finger 248, gate electrodefinger 238, field plate electrode finger 268, and drain electrode finger258. As shown, source electrode finger 248 is not continuous, andincludes multiple segments separated by gaps. Each segment of sourceelectrode finger 248 is electrically connected with metal 1 structure245 b through one or more vias (not shown). As shown, gate electrodefinger 238 includes projection portions which extend into the gapsbetween the segments of source electrode finger 248.

FIG. 4C is a plan view of metal 1 structures 255, 245 a, and 245 b. Asshown, metal 1 structure 245 b includes openings 249, and metal 1islands 243 within the openings 249. Openings 249 and metal 1 islands243 are formed in the metal 1 structure 245 b so as to overlap theprojection portions of gate electrode finger 238 which extend into thegaps between the segments of source electrode finger 248. In addition,metal 1 islands 243 are electrically connected with the projectionportions of gate electrode finger 238 by one or more vias (not shown).

FIG. 4D using plan view of metal 2 structures 257, 247, and 237. Metal 2structure 237 is formed so as to overlap metal 1 structure 245 b. Inaddition, metal 2 structure 237 is electrically connected with metal 1islands 243 through one or more vias (not shown).

Accordingly, metal 2 structure 257 is electrically connected with drainelectrode finger 258 of the sub-transistor through metal 1 structure255. In addition, metal 2 structure 247 is electrically connected withplate electrode finger 268 and source electrode finger 248 through metal1 structures 245 a and 245 b. Furthermore, metal 2 structure 237 iselectrically connected with gate electrode finger 238 through the metal1 islands 243 of metal 1 structure 245 b.

In some embodiments of integrated half bridge power conversion circuit100, either or both of power transistors 115 and 125 and theirrespective driver 120 and 130 may be implemented with a distributed orfingered topology. For example, FIG. 5 is a schematic illustration of adistributed transistor 300 connected with a distributed driver or driveroutput stage 400.

Distributed driver or driver output stage 400 includes sub-drivers 402,404, 406, and 408. Distributed transistor 300 may be similar todistributed transistor 200 of FIG. 2 and includes sub-transistors 302,304, 306, and 308. As shown, sub-drivers 402, 404, 406, and 408 haveinputs connected to the same signal IN The outputs, however, ofsub-drivers 402, 404, 406, and 408 are respectively connected with gateinputs of different sub-transistors 302, 304, 306, and 308. Becausesub-drivers 402, 404, 406, and 408 have identical or substantiallyidentical functionality, the outputs generated by sub-drivers 402, 404,406, and 408 are identical or substantially identical.

In some embodiments, sub-transistors 302, 304, 306, and 308 haveidentical or substantially identical sizes. In such embodiments,sub-drivers 402, 404, 406, and 408 may likewise have identical orsubstantially identical sizes.

In some embodiments, sub-transistors 302, 304, 306, and 308 do not haveidentical sizes. In such embodiments, sub-drivers 402, 404, 406, and 408may likewise not have identical sizes, but, instead, may have sizeswhich scale or correspond with the size of sub-transistors 302, 304,306, and 308. For example, sub-driver 402 may have a size correspondingwith or proportional to the size of sub-transistors 302, sub-driver 404may have a size corresponding with or proportional to the size ofsub-transistors 304, and sub-driver 406 may have a size corresponding orproportional to with the size of sub-transistors 306.

In some embodiments, each sub-driver of a distributed driver has anoutput which is connected to multiple sub-transistors. For example, eachsub-driver of a distributed driver may have an output which iselectrically connected to 2, 4, 8, or another number of sub-transistors.In such embodiments, the sub-transistors of the distributed power switchmay be spaced according to a first pitch, and the sub-drivers of thedistributed drive circuit are spaced according to a second pitch, andthe second pitch is equal to n times the first pitch, wherein n is aninteger.

Among other benefits, embodiments of integrated half bridge powerconversion circuit 100 having power transistors and their respectivedrivers implemented with a distributed topology have superior timingperformance. Because of the distributed topology, each segment of thepower transistor is turned on or off at substantially the same time.Without the distributed technology, the time at which each particularportion of the power transistor is turned on or off is dependent on thepropagation delay and arrival time of the controlling signal at eachparticular portion.

FIG. 6 is a schematic illustration of portion 450 of an embodiment of alayout of transistor 300 and driver or driver output stage 400. Theembodiment of FIG. 6 is provided as an example only. Numerousalternative layout configurations for transistor 300 are additionallycontemplated. To details of the layout of driver or driver output stage400 is not illustrated, as the inventive aspects apply equally to anydriver or driver output stage.

As shown, sub-drivers 402, 404, 406, and 408 are each connected to theinput signal IN with a conductor of identical length and impedance. Inaddition, sub-drivers 402, 404, 406, and 408 are respectively connectedgate electrodes of sub-transistors 302, 304, 306, and 308 with aconductor of identical length and impedance.

FIG. 7 is a simplified schematic of half bridge power conversion circuit100 having been modified to include low side pulldown FET 122 and highside pulldown FET 132. In some half bridge power conversion circuits,parasitic inductances and capacitances result in transient voltages atthe gate of low side transistor 115 and at the gate of high sidetransistor 125. Low side pulldown FET 122 is configured to be on whenlow side transistor 115 is off, such that the transient voltages at thegate of low side transistor 115 remain low enough that low sidetransistor 115 is not turned on as a result of the transient voltages.Similarly, high side pulldown FET 132 is configured to be on when highside transistor 125 is off, such that the transient voltages at the gateof high side transistor 125 remain low enough that high side transistor125 is not turned on as a result of the transient voltages.

In some embodiments, the low side pulldown FET 122 and high sidepulldown 132 advantageously help to reduce the voltages at the gates oflow side transistor 115 and high side transistor 125, such that low sidetransistor 115 and high side transistor 125 are turned off quickly, thusallowing for higher frequency operation.

FIG. 8 is a schematic illustration of a circuit 500 having a distributedtransistor and a distributed pulldown FET. The distributed transistor ofcircuit 500 includes sub-transistors 502, 504, 506, and 508. Thedistributed pulldown FET of circuit 500 includes sub-FETs 512, 514, 516,and 518. As shown, the gate of each sub-transistor is connected to thedrain of a corresponding sub-FET.

FIG. 9 a schematic illustration of an embodiment of a layout 520 ofcircuit 500. The embodiment of FIG. 9 is provided as an example only.Numerous alternative layout configurations for circuit 500 areadditionally contemplated.

The layout 520 illustrates the metal 2 drain D, source S, and gate Gstructures of circuit 500. The illustrated metal 2 drain D, source S,and gate G structures respectively correspond, for example, with metal 2structures 257, 247, and 237 discussed above with reference to FIGS.4A-4D.

The layout 520 also illustrates interconnect structure 510. Interconnectstructure 510 includes, for example, a metal 1 layer, a metal 2 layer,and vias connecting portions of the metal 1 layer with portions of themetal 2 layer. Interconnect structure 510 is configured to electricallyconnect metal 2 drain D structures of sub-transistors 512, 514, 516, and518 with metal 2 gate G structures of sub-transistors 502, 504, 506, and508, respectively. In addition, interconnect structure 500 is configuredto electrically connect metal 2 source S structures of sub-transistors512, 514, 516, and 518 with metal 2 source S structures ofsub-transistors 502, 504, 506, and 508, respectively.

In some embodiments, the orientation of sub-transistors 502, 504, 506,and 508 is reversed with respect to the orientation of sub-transistors512, 514, 516, and 518. In such embodiments, interconnect structure 510may comprise metal 2 jumpers configured to respectively make theappropriate connections between sub-transistors 502, 504, 506, and 508and sub-transistors 512, 514, 516, and 518.

FIG. 10 is a schematic illustration of a circuit 600 having adistributed transistor and pulldown FET 605, a distributed pulldown FETdriver 610, and a distributed transistor driver 620. The distributedtransistor and pulldown FET 605 of circuit 600 may be similar to circuit500 of FIG. 8.

The distributed pulldown FET driver 610 includes sub-drivers 612, 614,616, and 618. The distributed transistor driver 620 includes sub-drivers622, 624, 626, and 628. As shown, the gate of each sub-transistor of thedistributed transistor is connected to the output of a correspondingsub-driver of the distributed transistor driver 620. Additionally, thegate of each sub-FET of the distributed pulldown FET is connected to theoutput of a corresponding sub-driver of the distributed pulldown FETdriver 610.

In some embodiments of half bridge power conversion circuit 100, thedistributed transistor and pulldown FET 605 of circuit 600 correspondswith low side transistor 115 and low side pulldown FET 122. In suchembodiments, distributed transistor driver 620 corresponds with low sidetransistor drive circuit 120, and distributed pulldown FET driver 610corresponds with high side transistor drive circuit 130, as illustrated,for example, in FIG. 7.

In some embodiments of half bridge power conversion circuit 100, thedistributed transistor and pulldown FET 605 of circuit 600 correspondswith high side transistor 125 and high side pulldown FET 132. In suchembodiments, distributed transistor driver 620 corresponds with highside transistor drive circuit 130, and distributed pulldown FET driver610 corresponds with low side transistor drive circuit 120, asillustrated, for example, in FIG. 7.

In some embodiments of half bridge power conversion circuit 100, thegates of low side pulldown FET 122 and high side pulldown FET 132 arerespectively driven by inverter circuits having their inputsrespectively driven by low side transistor drive circuit 120 and highside transistor drive circuit 130.

FIG. 11 is a schematic illustration of a circuit 650, which includesdrive transistor 652, pulldown FET 653, and an inverter comprisingtransistor 654 and resistor 655. Circuit 650 also includes optionalZener diodes 656, which may provide overvoltage and/or ESD protection.

In some embodiments of half bridge power conversion circuit 100 as shownin FIG. 1, an instance of circuit 650 may be used instead of each of lowside transistor 115 and high side transistor 125.

As shown in FIG. 11, the Gate input signal is provided both to the gateof drive transistor 652 and to the gate of transistor 654 of theinverter. The output of the inverter is connected to the gate ofpulldown FET 653. Accordingly, if the drive transistor 652 is on as aresult of sufficient voltage at the Gate input, the output of theinverter turns off the pulldown FET 653 to allow for the drivetransistor 652 to be on. Similarly, if the drive transistor 652 is offas a result of insufficient voltage at the Gate input, the output of theinverter turns on the pulldown FET 653 to reduce the gate to sourceimpedance of the drive transistor 652. As a result of the pulldown FET653 being on, transient voltages at the Gate input are minimized bypulldown FET 653 to be sufficiently low that the drive transistor 652does not unwantedly turn on as a result of the transient voltages.

FIG. 12 is a simplified schematic of half bridge power conversioncircuit 100 having been modified to include diodes 124 and 134. In 124and 134 have anodes respectively connected to the sources of low sidetransistor 115 and high side transistor 125. In addition, 124 and 134have cathodes respectively connected to the drains of low sidetransistor 115 and high side transistor 125. Diodes 124 and 134 arerespectively configured to conduct current from the sources of low sidetransistor 115 and high side transistor 125 to the drains of low sidetransistor 115 and high side transistor 125 if, for example, aninductive load causes current to flow in the opposite direction.

Without diode 124, the inductive load may cause the voltage at the nodeVsw to go significantly below ground before low side transistor 115turns on. Once on, low side transistor 115 clamps the voltage at thenode Vsw to a voltage about equal to a transistor threshold belowground. Similarly, without diode 134, the inductive load may cause thevoltage at the node Vsw to go significantly above V+ before high sidetransistor 125 turns on. Once on, high side transistor 125 clamps thevoltage at the node Vsw to a voltage about equal to a transistorthreshold above V+.

In contrast, with diodes 124 and 134 the voltage at the node Vsw isclamped to a diode threshold below ground and a diode threshold aboveV+. With diodes 124 and 134, current flows earlier or at less extremevoltages. To turn on diode 124, the voltage induced by the inductiveload at the node Vsw must go lower than a diode threshold below ground.Similarly, to turn on diode 134, the voltage induced by the inductiveload at the node Vsw must go above a diode threshold above V+. Becausethe diode threshold of diodes 124 and 134 is less than the transistorthreshold voltages of low side transistor 115 and high side transistor125, with diodes 124 and 134, the voltage at the node Vsw is clamped toa more preferable smaller range.

In some embodiments, diodes 124 and 134 may be distributed, for example,as part of a distributed implementation of low side transistor 115 orhigh side transistor 125, for example, as discussed below in furtherdetail.

FIG. 13 is a schematic illustration of a circuit 690 having adistributed transistor and a distributed diode. The distributed diodehas its anode connected to the source of the distributed transistor andits cathode connected to the drain of the distributed transistor. Thedistributed transistor includes sub-transistors 692, and the distributeddiode includes sub-diodes 693. In this embodiment, there is onesub-diode for every two sub-transistors. In other embodiments, there isone sub-diode for every fewer or more sub-transistors.

FIG. 14 is a schematic illustration of a portion 700 of an embodiment ofa layout of circuit 690. The embodiment of FIG. 14 is provided as anexample only. Numerous alternative layout configurations for circuit 690are additionally contemplated.

Source electrode fingers 741, 742, 743, and 744 each form an ohmiccontact with an underlying AlGaN or similar layer and collectively formthe source electrode of the distributed transistor of circuit 690.Source electrode fingers 741, 742, 743, and 744 respectively form thesource electrodes of sub-transistors 692. The source electrode fingers741, 742, 743, and 744 are electrically connected to one another and toone or more pins through one or more conductors (not shown). In someembodiments, source electrode fingers 743, and 744 are electricallyconnected to one another and to one or more pins through overlyingmetallization layers.

Drain electrode fingers 751, 752, 753, 754, 755, and 756 each form anohmic contact with the underlying AlGaN or similar layer andcollectively form the drain electrode of the distributed transistor ofcircuit 690. Drain electrode fingers 751, 752, 753, 754, 755, and 756respectively form the drain electrodes of sub-transistors 692. The drainelectrode fingers 751, 752, 753, 754, 755, and 756 are electricallyconnected to one another and to one or more pins through one or moreconductors (not shown). In some embodiments, drain electrode fingers751, 752, 753, 754, 755, and 756 are electrically connected to oneanother and to one or more pins through overlying metallization layers.

Gate electrode fingers 731, 732, 733, and 734 are separated from theAlGaN or similar layer by respective gate structures. Gate structurescorresponding with insulated gates, Schottky gates, PN gates, recessedgates, and other gates may be used. Gate electrode fingers 731, 732,733, and 734 collectively form the gate electrode of the distributedtransistor of circuit 690, and respectively form the gates electrodes ofsub-transistors 692. Gate electrode fingers 731, 732, 733, and 734 areelectrically connected to one another and to one or more pins throughone or more conductors (not shown). In some embodiments, gate electrodefingers, 731, 732, 733, and 734 are electrically connected to oneanother and to one or more pins through overlying metallization layers.

Field plate electrode fingers 761, 762, 764, and 765 are separated fromthe AlGaN or similar layer by respective insulation structures, andcollectively form a field plate electrode of the distributed transistorof circuit 690. Field plate electrode fingers 761, 762, 764, and 765respectively form field plate electrodes of sub-transistors 692. Fieldplate electrode fingers 761, 762, 764, and 765 are electricallyconnected to one another and to one or more pins through one or moreconductors (not shown). In some embodiments, field plate electrodefingers 761, 762, 764, and 765 are electrically connected to one anotherand to one or more pins through overlying metallization layers.

Diode electrode fingers 748 and 749 form diodes 693 of circuit 690.

FIG. 15 a schematic illustration of a cross section of portion 700 takenalong the top or bottom edge of FIG. 14. Source electrode fingers 741,742, 743, and 744, drain electrode fingers 751, 752, 753, 754, 755, and756, gate electrode fingers 731, 732, 733, and 734, and field plateelectrode fingers 761, 762, 764, and 765 are similar to thecorresponding structures of, for example, transistor 200, as illustratedin FIG. 3B.

In this embodiment, every third sub-transistor functions as a sub-diodeof the distributed diode because its gate is connected to its source. Asshown in FIG. 15, diode electrode fingers 748 and 749 contact the AlGaNor similar layer and overly the gate structure, thereby forming gate tosource connections. In this embodiment, diode electrode fingers 748 and749 also form the filed plates of the diode connected sub-transistors.

In alternative embodiments, diode connected sub-transistors havecross-sectional architecture which is identical to that of transistor200, as illustrated in FIG. 3B. in such embodiments, Gates and sourcesof the sub-transistors are connected, for example, in the additionalmetallization overlying the sub-transistors.

FIG. 16 a schematic illustration of a cross section of portion 700 takenalong the top or bottom edge of FIG. 14. Source electrode fingers 741,742, 743, and 744, drain electrode fingers 751, 752, 753, 754, 755, and756, gate electrode fingers 731, 732, 733, and 734, and field plateelectrode fingers 761, 762, 764, and 765 are similar to thecorresponding structures of, for example, transistor 200, as illustratedin FIG. 3B.

In this embodiment, the gate structure of every third sub-transistor isomitted. In place of the omitted gate structures, Schottky barriers arerespectively formed at the junctions of the AlGaN or similar layer andSchottky structures 750 and 755 beneath diode electrode fingers 748 and749. Schottky structures comprise a Schottky metal. In some embodiments,diode electrode fingers 748 and 749 comprise a Schottky metal and arerespectively integrated with Schottky structures 750 and 755.

FIG. 17 is a flowchart diagram illustrating an embodiment of a method800 of forming a distributed transistor integrated with a distributeddriver.

At 810, a distributed transistor is formed. For example, a transistorhaving fingered gates and fingered sources may be formed by formingmultiple adjacent sub-transistors each including a source and a gate. Insome embodiments, the sources of the sub-transistors are electricallyconnected with a conductor. In some embodiments, the gates of thesub-transistors are electrically connected with a conductor. In someembodiments, the sub-transistors share a collective drain connection. Insome embodiments, the sub transistors each have a separate drainconnection.

At 820, a distributed driver is formed. The distributed driver includesat least an output stage which is distributed. For example, the outputstage of the driver may include a distributed pull up transistor and adistributed pulldown transistor, where the distributed pull uptransistor includes multiple pull up sub-transistors and the distributedpulldown transistor includes multiple pull down sub-transistors. In someembodiments, other or all portions of the distributed driver or alsodistributed.

In some embodiments, the distributed pull up transistor and thedistributed pulldown transistor are formed using a process similar tothat described at 810. In some embodiments, sources of the pull upsub-transistors are each connected with a drain of a corresponding oneof the pulldown sub-transistors with a conductor. Each pair ofcorresponding pull up and pulldown sub-transistors forms a sub-driverhaving an output electrode formed by the conductor connecting the sourceof the pull up sub-transistor and the drain of the pulldownsub-transistor thereof.

In some embodiments, the distributed pull up transistor, the distributedpulldown transistor, and the distributed transistor of 810 are formedhaving the same pitch. In such embodiments, each sub-transistor of thedistributed transistor of 810 may be aligned with a pair ofcorresponding pull up and pulldown sub-transistors forming a sub-driver.

At 830, the outputs of the distributed driver are connected to thefingered gates of the distributed transistor. For example, the gates ofthe sub-transistors of the distributed transistor may each be connectedto an output electrode of a corresponding sub-driver with a conductor.In some embodiments, the conductor connecting the gates of thesub-transistors to the output electrodes of the sub-drivers is the sameconductor as that connecting the sources of the pull up sub-transistorswith the drains of the pulldown sub-transistors of the sub-drivers.

FIG. 18 is a flowchart diagram illustrating an embodiment of a method900 of forming first and second distributed transistors.

At 910, a first distributed transistor is formed. For example, a firsttransistor having fingered gates and fingered sources may be formed byforming multiple adjacent sub-transistors each including a source and agate. In some embodiments, the sources of the sub-transistors areelectrically connected with a conductor. In some embodiments, the gatesof the sub-transistors are electrically connected with a conductor. Insome embodiments, the sub-transistors share a collective drainconnection. In some embodiments, the sub transistors each have aseparate drain connection.

At 920, a second distributed transistor is formed. For example, a secondtransistor having fingered gates and fingered sources may be formed byforming multiple adjacent sub-transistors each including a source and agate. In some embodiments, the sources of the sub-transistors areelectrically connected with a conductor. In some embodiments, the gatesof the sub-transistors are electrically connected with a conductor. Insome embodiments, the sub-transistors share a collective drainconnection. In some embodiments, the sub transistors each have aseparate drain connection.

In some embodiments, the first distributed transistor and the seconddistributed transistor are formed having the same pitch. In suchembodiments, each sub-transistor of the first distributed transistor maybe aligned with one of the sub-transistors of the second distributedtransistor.

At 930, the first distributed transistor is connected to the seconddistributed transistor. For example, if the gates of the sub-transistorsof the first distributed transistor may be connected by a firstconductor with a collective drain of the second distributed transistor.In addition, the sources of each of the sub-transistors of the firstdistributed transistor may be connected by a second conductor with thesources of the sub-transistors of the second distributed transistor.

In some embodiments, the first distributed transistor may be formed witha first driver using a method such as method 800 described above. Insome embodiments, the second distributed transistor be formed with asecond driver using a method such as method 800 describe above.

FIG. 19 is a flowchart diagram illustrating an embodiment of a method1000 of forming a distributed transistor and a distributed diode.

At 1010, a distributed transistor is formed. For example, a transistorhaving fingered gates and fingered sources may be formed by formingmultiple sub-transistors each including a source and a gate. In someembodiments, the sources of the sub-transistors are electricallyconnected with a conductor. In some embodiments, the gates of thesub-transistors are electrically connected with a conductor. In someembodiments, the sub-transistors share a collective drain connection. Insome embodiments, the sub transistors each have a separate drainconnection.

At 1020, a distributed diode is formed. For example, a fingered diodemay be formed such that the fingers of the fingered diode areinterleaved with the fingered gates and sources of the sub-transistorsof the distributed transistor. In some embodiments, the distributeddiode is formed by electrically connecting gates and sources of some ofthe sub-transistors of the distributed transistor. In some embodiments,the distributed diode is formed by connecting a Schottky metal to thedrain of the distributed transistor in multiple locations.

At 1030, the distributed transistor is connected to the distributeddiode. For example, the anodes of the sub-diodes may be connected withthe sources of each of one or more sub-transistors of the distributedtransistor, and the cathodes of the sub-diodes may be connected with thedrain of the distributed transistor.

In some embodiments, the anodes of the sub-diodes are connected with thesources of each of one or more sub-transistors of the distributedtransistor by electrically connecting the gates and sources of some ofthe sub-transistors of the distributed transistor. In some embodiments,the anodes of the sub-diodes are connected with the sources of each ofone or more sub-transistors on the distributed transistor byelectrically connecting the Schottky metal/drain junctions of thedistributed diode to the sources of each of one or more sub-transistorsof the distributed transistor.

In some embodiments, the distributed transistor may be formed with adriver using a method such as method 800 described above. In someembodiments, the distributed transistor and the distributed diode may beformed with a driver using a method such as method 800 described above.In some embodiments, the distributed transistor may be formed with asecond distributed transistor using a method such as method 900described above.

FIG. 20 is a flowchart diagram illustrating an embodiment of a method1100 of forming a distributed transistor.

At 1110, a distributed transistor is formed. For example, a transistorhaving fingered gates and fingered sources may be formed by formingmultiple sub-transistors each including a source and a gate.

At 1120, ohmic contacts to the gates and sources of the sub-transistorsare formed by respectively contacting the gates and sources of thesub-transistors with ohmic gate and source conductors. In someembodiments, the gates of the sub-transistors are electrically connectedto one another with a conductor. In some embodiments, the sources of thesub-transistors are electrically connected to one another with aconductor. In some embodiments, the sub-transistors share a collectivedrain connection. In some embodiments, the sub-transistors each have aseparate drain connection.

At 1130, a first additional conductive layer is formed. In someembodiments, the first additional conductive layer at least partiallycovers and electrically contacts the ohmic contact of the gates of thesub-transistors through one or more vias. In some embodiments, the firstadditional conductive layer at least partially covers and electricallycontacts the ohmic contact of the sources of the sub-transistors throughone or more vias.

At 1140, a second additional conductive layer is formed. In someembodiments, the second additional conductive layer at least partiallycovers and electrically contacts the ohmic contact of the gates of thesub-transistors through one or more vias and through an opening in thefirst additional conductive layer. In some embodiments, the secondadditional conductive layer at least partially covers and electricallycontacts the ohmic contact of the gates of the sub-transistors throughone or more vias and through an opening in the first additionalconductive layer.

In some embodiments, the ohmic gate conductor overlaps the sources ofthe sub-transistors. In some embodiments, the second additionalconductive layer electrically contacts the ohmic contact of the gates ofthe sub-transistors and a portion of the ohmic conductor which overlapsthe sources of the sub-transistors.

In some embodiments, the distributed transistor may be formed with adriver using a method such as method 800 described above. In someembodiments, the distributed transistor may be formed with a seconddistributed transistor using a method such as method 900 describedabove.

Each of the circuits discussed herein include one or more inventivefeatures. The various features of the circuits may be applied to otherembodiments of circuits in combinations of features which arecontemplated, but not specifically discussed for the sake of brevity.

The various aspects of the devices discussed herein may be practiced inother semiconductor technologies. For example, the various aspects ofthe devices discussed herein may be practiced in Silicon, Germanium,Gallium Arsenide, Silicon Carbide, Organic, and other technologies.

While various embodiments of present invention have been described, itwill be apparent to those of skill in the art that many more embodimentsand implementations are possible that are within the scope of thisinvention. Accordingly, the present invention is not to be restrictedexcept in light of the attached claims and their equivalents.

What is claimed is:
 1. An electronic circuit, comprising: a substratecomprising GaN; a distributed power switch formed on the substrate,wherein the distributed power switch comprises a plurality of powersub-transistors, and wherein each power sub-transistor comprises a gate,a source, and a drain; and a distributed diode formed on the substrate,wherein the distributed diode comprises a plurality of sub-diodes,wherein each sub-diode comprises an anode, and a cathode, wherein theanodes of the sub-diodes are each connected to a source of one or morecorresponding power sub-transistors, and wherein the cathodes of thesub-diodes are each connected to a drain of one or more correspondingpower sub-transistors.
 2. The electronic circuit of claim 1, wherein thedistributed diode is formed by electrically connecting a gate and asource of each of a plurality of sub-transistors of the distributedpower switch with a conductor.
 3. The electronic circuit of claim 1,wherein the distributed diode is formed by electrically connecting asource electrode of at least two of the sub-transistors of thedistributed power switch to the substrate with a Schottky metal.
 4. Theelectronic circuit of claim 1, further comprising a distributed drivecircuit formed on the substrate, wherein the distributed drive circuitcomprises a distributed output stage formed by a plurality ofsub-drivers, wherein each sub-driver comprises an input and an output,and wherein the output of each sub-driver is connected to a gate of oneor more corresponding sub-transistors of the sub-transistors of thedistributed power switch.
 5. The electronic circuit of claim 4, furthercomprising a distributed pulldown transistor formed on the substrate,wherein the distributed pulldown transistor comprises a plurality ofpulldown sub-transistors, wherein each pulldown sub-transistor comprisesa gate, a source, and a drain, wherein the gates of the pulldownsub-transistors are electrically connected together, wherein the sourcesof the pulldown sub-transistors are each connected to a source of one ormore corresponding power sub-transistors, and wherein the drains of thepulldown sub-transistors are each connected to a gate of thecorresponding power sub-transistors.
 6. The electronic circuit of claim5, further comprising: a first conductor connected to the gates of thepower sub-transistors; a second conductor connected to the sources ofthe power sub-transistors; a third conductor overlapping at least aportion of the second conductor, wherein the third conductor comprises:a first portion connected to the second conductor with one or more vias,and a second portion connected to the first conductor with one or morevias; and a fourth conductor overlapping the second portion of the thirdconductor, and connected to the first conductor by the second portion ofthe third conductor, wherein the fourth conductor has a thickness of atleast 2 microns.
 7. The electronic circuit of claim 4, furthercomprising: a first conductor connected to the gates of the powersub-transistors; a second conductor connected to the sources of thepower sub-transistors; a third conductor overlapping at least a portionof the second conductor, wherein the third conductor comprises: a firstportion connected to the second conductor with one or more vias, and asecond portion connected to the first conductor with one or more vias;and a fourth conductor overlapping the second portion of the thirdconductor, and connected to the first conductor by the second portion ofthe third conductor, wherein the fourth conductor has a thickness of atleast 2 microns.
 8. The electronic circuit of claim 1, furthercomprising a distributed pulldown transistor formed on the substrate,wherein the distributed pulldown transistor comprises a plurality ofpulldown sub-transistors, wherein each pulldown sub-transistor comprisesa gate, a source, and a drain, wherein the gates of the pulldownsub-transistors are electrically connected together, wherein the sourcesof the pulldown sub-transistors are each connected to a source of one ormore corresponding power sub-transistors, and wherein the drains of thepulldown sub-transistors are each connected to a gate of thecorresponding power sub-transistors.
 9. The electronic circuit of claim8, further comprising: a first conductor connected to the gates of thepower sub-transistors; a second conductor connected to the sources ofthe power sub-transistors; a third conductor overlapping at least aportion of the second conductor, wherein the third conductor comprises:a first portion connected to the second conductor with one or more vias,and a second portion connected to the first conductor with one or morevias; and a fourth conductor overlapping the second portion of the thirdconductor, and connected to the first conductor by the second portion ofthe third conductor, wherein the fourth conductor has a thickness of atleast 2 microns.
 10. The electronic circuit of claim 1, furthercomprising: a first conductor connected to the gates of the powersub-transistors; a second conductor connected to the sources of thepower sub-transistors; a third conductor overlapping at least a portionof the second conductor, wherein the third conductor comprises: a firstportion connected to the second conductor with one or more vias, and asecond portion connected to the first conductor with one or more vias;and a fourth conductor overlapping the second portion of the thirdconductor, and connected to the first conductor by the second portion ofthe third conductor, wherein the fourth conductor has a thickness of atleast 2 microns.
 11. An electronic component, comprising: a packagebase; and at least one GaN-based die secured to the package base andincluding an electronic circuit comprising: a substrate comprising GaN;a distributed power switch formed on the substrate, wherein thedistributed power switch comprises a plurality of power sub-transistors,and wherein each power sub-transistor comprises a gate, a source, and adrain; and a distributed diode formed on the substrate, wherein thedistributed diode comprises a plurality of sub-diodes, wherein eachsub-diode comprises an anode, and a cathode, wherein the anodes of thesub-diodes are each connected to a source of one or more correspondingpower sub-transistors, and wherein the cathodes of the sub-diodes areeach connected to a drain of one or more corresponding powersub-transistors.
 12. The electronic component of claim 11, wherein thedistributed diode is formed by electrically connecting a gate and asource of each of a plurality of sub-transistors of the distributedpower switch with a conductor.
 13. The electronic component of claim 11,wherein the distributed diode is formed by electrically connecting asource electrode of at least two of the sub-transistors of thedistributed power switch to the substrate with a Schottky metal.
 14. Theelectronic component of claim 11, wherein the electronic circuit furthercomprises a distributed drive circuit formed on the substrate, whereinthe distributed drive circuit comprises a distributed output stageformed by a plurality of sub-drivers, wherein each sub-driver comprisesan input and an output, and wherein the output of each sub-driver isconnected to a gate of one or more corresponding sub-transistors of thesub-transistors of the distributed power switch.
 15. The electroniccomponent of claim 14, wherein the electronic circuit further comprisesa distributed pulldown transistor formed on the substrate, wherein thedistributed pulldown transistor comprises a plurality of pulldownsub-transistors, wherein each pulldown sub-transistor comprises a gate,a source, and a drain, wherein the gates of the pulldown sub-transistorsare electrically connected together, wherein the sources of the pulldownsub-transistors are each connected to a source of one or morecorresponding power sub-transistors, and wherein the drains of thepulldown sub-transistors are each connected to a gate of thecorresponding power sub-transistors.
 16. The electronic component ofclaim 15, wherein the electronic circuit further comprises: a firstconductor connected to the gates of the power sub-transistors; a secondconductor connected to the sources of the power sub-transistors; a thirdconductor overlapping at least a portion of the second conductor,wherein the third conductor comprises: a first portion connected to thesecond conductor with one or more vias, and a second portion connectedto the first conductor with one or more vias; and a fourth conductoroverlapping the second portion of the third conductor, and connected tothe first conductor by the second portion of the third conductor,wherein the fourth conductor has a thickness of at least 2 microns. 17.The electronic component of claim 14, wherein the electronic circuitfurther comprises: a first conductor connected to the gates of the powersub-transistors; a second conductor connected to the sources of thepower sub-transistors; a third conductor overlapping at least a portionof the second conductor, wherein the third conductor comprises: a firstportion connected to the second conductor with one or more vias, and asecond portion connected to the first conductor with one or more vias;and a fourth conductor overlapping the second portion of the thirdconductor, and connected to the first conductor by the second portion ofthe third conductor, wherein the fourth conductor has a thickness of atleast 2 microns.
 18. The electronic component of claim 11, wherein theelectronic circuit further comprises a distributed pulldown transistorformed on the substrate, wherein the distributed pulldown transistorcomprises a plurality of pulldown sub-transistors, wherein each pulldownsub-transistor comprises a gate, a source, and a drain, wherein thegates of the pulldown sub-transistors are electrically connectedtogether, wherein the sources of the pulldown sub-transistors are eachconnected to a source of one or more corresponding powersub-transistors, and wherein the drains of the pulldown sub-transistorsare each connected to a gate of the corresponding power sub-transistors.19. The electronic component of claim 18, wherein the electronic circuitfurther comprises: a first conductor connected to the gates of the powersub-transistors; a second conductor connected to the sources of thepower sub-transistors; a third conductor overlapping at least a portionof the second conductor, wherein the third conductor comprises: a firstportion connected to the second conductor with one or more vias, and asecond portion connected to the first conductor with one or more vias;and a fourth conductor overlapping the second portion of the thirdconductor, and connected to the first conductor by the second portion ofthe third conductor, wherein the fourth conductor has a thickness of atleast 2 microns.
 20. The electronic component of claim 11, wherein theelectronic circuit further comprises a first conductor connected to thegates of the power sub-transistors; a second conductor connected to thesources of the power sub-transistors; a third conductor overlapping atleast a portion of the second conductor, wherein the third conductorcomprises: a first portion connected to the second conductor with one ormore vias, and a second portion connected to the first conductor withone or more vias; and a fourth conductor overlapping the second portionof the third conductor, and connected to the first conductor by thesecond portion of the third conductor, wherein the fourth conductor hasa thickness of at least 2 microns.